The present invention generally relates to ultrasonic transducers, and in particular relates to the protection of ultrasonic probes from electromagnetic (EM) or radio frequency (RF) interference.
Ultrasound diagnostic technology generally relates to imaging of biological tissue within an animal body, typically human, using an ultrasound transducer. An ultrasound transducer transmits ultrasonic waves into the tissue and receives ultrasonic echoes which are reflected from the tissue. The transducer may be placed on a body surface or inserted into a patient""s body in a selected imaging region, for example, the esophagus. Simply described, transducers include ultrasound sensors, a housing and cabling to connect the transducer to the rest of the ultrasound imaging system. Sensors may be described as including one or more piezoelectric elements, impedance matching material (stack) and required mechanical components. There are single element sensors (single channel), and multi-element sensors (multi-channel), comprising sensor arrays, which actually generate and direct ultrasonic waves to the imaging region. More particularly, piezoelectric element(s) in the transducer sensor portion transmit the ultrasonic waves and then receive the return echoes reflected from the imaging region. The piezoelectric elements contained in the transducer convert the received acoustic waves into electrical signals that are processed to form a diagnostic image.
Transesophageal echocardiography (TEE) probes are specific ultrasound transducers which are used endoscopically, for example, for ultrasonic imaging of the heart. Ultrasound imaging of the heart is always a difficult task because the heart is located in the thoracic cavity surrounded by the ribs and lungs. Ultrasound imaging through the ribs is difficult because of the absorptive and reflective characteristics of the bone structure comprising the ribs. This requires access through any of several intercostal windows, but even the transmission and reception of ultrasound through intercostal windows may provide ultrasound data with limited clinical use.
TEE probes were developed through application of the general body of endoscopic technology (introduction of medical devices into the body) to ultrasound in order to overcome the problems associated with imaging thoracic organs mentioned briefly above. TEE probes include an ultrasonic sensor located at the end or tip of an elongated probe housing. The TEE probe may be passed through the patient""s mouth into the esophagus or stomach. When inserted orally into the stomach or esophagus within the thoracic cavity, the ribs no longer pose an impediment to the transmission and reception of ultrasound signals. The typical TEE probe includes a control mechanism external to the body, enabling the clinician to manipulate the end of the probe so that the sensor or transducer array at the end or tip of the probe is directed as desired towards, for example, the heart, and is a significant improvement in the use of ultrasound to diagnose the heart.
U.S. Pat. No. 4,543,960, the contents of which are incorporated herein by reference, teaches a TEE ultrasound transducer probe in which a phased array or linear array of transducer elements is mounted on a rotating base inside the probe assembly. As shown in the drawings accompanying the patent, the transducer array is formed of a rectangular shaped array of piezoelectric elements mounted on a cylindrical rotateable base. A pulley is mounted on a shaft extending from the rotateable base, whereby the transducer array and base may be rotated inside the probe assembly varying the imaging plane. Improvements to U.S. Pat. No. 4,543,960 are described in U.S. Pat. No. 5,226,422, include a circular array transducer using improved grounding techniques, a bell-shaped housing for the transducer and a bubble trap for the transducer components, also incorporated herein in its entirety.
U.S. Pat. No. 5,555,887, commonly owned and incorporated herein in its entirety, discloses a TEE probe (or transducer probe assembly) which includes a removable articulating tip which allows the clinician to change the acoustic performance simply by replacing the probe tip. The articulation mechanism includes a plurality of links which snap together to form a continuous, torsionally stiff articulating joint. The joint has built in angulation stops and exhibits substantially no torsional play when loaded. The transducer in the probe assembly, more particularly, the probe tip, is rotated by a motor driven mechanism with two speeds of rotation. The transducer includes heat dissipating means for taking heat away from the Transducer probe.
TEE probes have been found to be useful in imaging the heart chambers in the operating room (OR) during surgical procedures, particularly in surgical interventions. OR imaging, however, must address the problem of electrical noise generated by surgical instrument use. For example, surgical procedure are often accompanied with surgical interventions including the use of electro-surgical units (ESUs) (e.g., cauterizing instruments). ESUs often generate high levels of broad spectrum electromagnetic energy which is dispersed into the surrounding environment, and are typically radiating at less than a body""s length away from a TEE or other transducer probe. This broad spectrum radiation dispersed by an active ESU, as well as other electromagnetic or RF noise (e.g., telemetry signals), may be coupled into the ultrasound equipment in the OR, or other clinical setting.
Conventional ultrasound systems are known to inadvertently receive such noise via whatever antenna-like apparatus (e.g., cables, interconnects) or antenna-emulating circuitry included in the ultrasound equipment. TEE probes are inherently good receiving antenna, because they include a relatively long cable connected between the probe and imaging system. The end result in any case is an inability of ultrasound diagnostic imaging to be utilized during ESU usage, or other high noise environments. This may include pre-operative assessment, postoperative assessment, or any time during actual surgery or other interventional procedure where an ESU or other noise generators are operating.
While attempts have been made to shield transducers from broadband RF radiation, no efforts are known herebefore to be effective, particularly for transducers or transducer probes used in the OR concurrently with the used of interventional equipment. Insufficient or incomplete electric shielding allows RF or EM energy to be coupled onto ultrasound coaxial and other electrical cables and circuits found within transducer housings. The coupled (received) energy makes its way into the ultrasound imaging system. If signal filters are not employed (which are not only expensive but take up precious space), ESU or other noise will be processed along with non-rejected imaging data and displayed on the imaging system display, complicating diagnoses.
It is therefore an object of this invention to provide an electromagnetically shielded transducer and/or transducer probe, as well as their respective assemblies, in order to avoid electromagnetic interference (EMI), for example, interference from radio frequency (RF) signals, RF interference or interference from electrical signals.
It is therefore an object of this invention to provide an electromagnetically shielded transducer and/or transducer probe, as well as their respective assemblies, in order to avoid any EM interference, regardless of its source or species, and particularly that generated proximate an ultrasound probe/system such as OR equipment (e.g., an ESU).
It is another object of this invention to provide an electromagnetically shielded transducer probe and/or assembly which is effectively shielded from EMI (RFI). We define transducer probe herein as a species of transducer, where TEE probes are a species of transducer probe.
It is another object of the invention to provide a transducer probe which is sufficiently shielded to essentially eradicate noise broad band, for example, at least 100 dB down broad spectrum, or at least at frequencies where particularly troubling noise may be found, e.g., frequency emitted from an ESU, as well as flexible enough in its gastroscopic portions to be useful.
One embodiment of this invention includes a transducer or transducer assembly in which all transducer components, which may include the sensor, sensor stack, transducer array, sensor interconnects, cabling housing and system interconnects, are entirely shielded. Any shield comprising what may be referred to as a system of shield to entirely shield every transducer component is preferably connected to ground (whether floating or earth ground) to minimize the impedance of the shield to current flow, thereby maximizing the shielding effect of same.
One embodiment of a transducer probe of this invention include that every component from a transducer connector to the endoscopic portion be completely shielded whereby the shield is implemented in such a manner as to maintain maximum flexibility.